This paper introduces a differentiated USB interrupt service framework for real-time systems, designed to provide predictable throughput and latency for I/O requests with different priority and criticality requirements. Implemented in the Quest RTOS using an xHCI USB 3.x driver, the approach associates separate USB interrupters with time-budgeted I/O VCPUs, allowing interrupt processing to match the priority of the tasks that depend on it. The framework provides temporal isolation between I/O workloads and improves predictability compared with conventional interrupt handling, including Linux with PREEMPT_RT and SCHED_DEADLINE.